Effect of different nanofluids on performance analysis of flat plate solar collector

Flat plate solar collectors are widely utilized for water heating in residential buildings, commercial and industrial applications. The thermal characteristics improvement of the working fluid can dramatically increase solar collector thermal efficiency. The working fluid thermal properties were improved by using nanofluids. Present work aims to study the effect of nano aluminum and titanium oxides addition to the water as a working fluid on solar collector efficiency. Outdoor experiments were carried out according to ASHRAE Standard 86 - 93. Nanoparticles of 25 nm size were used to reduce the agglomeration and increase the dispersion. Nanofluids were prepared at a concentration of 2% by weight and a surfactant was added to improve the stability. The tank outlet temperature was measured at different nanofluid flow rates of 2, 4, and 6 l/m. The maximum increases in tank outlet temperature for Al2O3 and TiO2 were 5 and 7% at a flow rate of 2 l/m, respectively. Al2O3 and TiO2 nanofluid improved the collector efficiencies by 30 and 32% at 2 l/m, respectively. TiO2 had an increase in collector efficiency about Al2O3 at all flow rates. The maximum improvements in thermal conductivity for TiO2 about Al2O3 were 1, 2, and 2.5% at 2, 4, and 6 l/m flow rates. The increases of friction coefficients of the nanofluids were less than 1% at all temperature range. The maximum increase in collector efficiency for Al2O3 and TiO2 were about 22 and 30%, respectively about base fluid. Using Al2O3 and TiO2 nanofluid was recommended to enhance solar collector performance.